On inclusion, comorbidities associated with obesity will be recorded. After recording of the informed consent patients will be randomized in two groups: usual care or intra-gastric balloon. In the latter, a second randomization will be performed between air-filled balloon or water-filled balloon. Six months later, after withdrawal of the balloon (if required), laparoscopic gastric by-pass will be performed. Thereafter, patients will be followed during 6 months.

The main criteria of judgement is the rate of admission in ICU during more than 24 hrs during the 30 days following surgery.

The secondary criteria of judgement is: the differences in pre-operative weight loss between the 2 groups, number of complications occurring during the 30 days after surgery, differences in different scales of quality of life (SF36, IWQOL-lite), differences in operative time, length of hospital stay, readmissions, and medical cots between the two strategies. Efficacy and tolerance of each type of balloon (air-filled or water-filled) will be compared in the intra-gastric balloon group.